A surface mounting electronic component, such as integrated circuit (IC), transistor, diode, condenser, and piezoelectric resistor, is supplied after being packaged in an electronic part package including a tray having an embossed pocket which can conform the shape of an electronic part or a carrier tape which continuously includes the embossed pockets, and a cover tape which can be heat-sealed on the tray or the carrier tape.
The carrier tape in which electronic parts are packaged is generally wound onto a reel made of paper or plastic, and the condition is maintained before mounting. In a mounting process, the electronic parts which are the contents stored in pockets are automatically removed from the pockets in the carrier tape or the tray from which the cover tape has been delaminated, and surface-mounted onto electronic circuit boards.
In recent years, as down-sizing and high functionality are accelerating, in order to improve productivity by reducing heat-sealing time, heat-sealing temperature or heat-sealing pressure are adjusted to be higher or larger than before.
In addition, it is necessary to mold the shape of the pocket in the carrier tape so as to be smaller. For this reason, the workability and strength of the pocket are improved by changing the material for the carrier tape from polystyrene-based material which has been used to engineering plastics, such as a polycarbonate-based resin having a high rigidity.
However, since the engineer plastics have a higher softening temperature than that of polystyrene, it is necessary to increase the heat-sealing temperature to higher than before in order to securely adhere the carrier tape and the cover tape.
Due to the request for improvement of productivity and the change of the material for the cover tape, it is examining that the temperature setting for heat-sealing the cover tape to the carrier tape is increased from the conventional heat-sealing temperature in a range of 120° C. to 160° C. to a higher temperature range of about 180° C. to about 220° C.
However, while the heat-sealing temperature is increasing, when the softening temperature of the material for the cover tape is lower, there is a problem in which a sealing trowel is contaminated in heat-sealing. In addition, when the softening temperature of a cushion layer is low, the thickness of the cushion layer is decreased due to flow of the resin of the cushion layer. Thereby, there is a problem in that the strength of the cover tape itself is decreased.
A method for preventing the contamination of the sealing trowel, a method for preventing the flow of the resin by increasing the heat resistance of the cushion layer is disclosed in Patent Document 1.
In addition, Patent Document 2 discloses a method for widening the heat-sealing temperature range by improving the sealing layer. However, when the sealing time is reduced in such a cover tape, there is a problem in that the stability of the peeling strength is not sufficient.
In addition, when heat-sealing is carried out, the temperature of sealing trowel is sometimes decreased immediately after production starts or production restarts. Furthermore, it is well known that the temperature of the sealing trowel varies depending on the surrounding environment during production. The temperature variation of the sealing trowel causes the variation of peeling strength of the cover tape. The variation of the peeling strength sometimes results in defective mounting of parts.    [Patent Document 1] PCT International Publication No. WO 10/018791    [Patent Document 2] PCT International Publication No. WO 07/123241